Japanese Patent Publication No. 3417127 discloses a drive circuit for a power converter. In the known drive circuit, a first frequency signal and a second frequency signal are outputted while they are switched at every preset period. The first and second frequency signals are alternately applied to the primary coil of a transformer, so that different voltages based on the first and second frequency signals are alternately induced across the secondary coil of the transformer with the secondary coil and the primary coil being electrically insulated.
The known drive circuit uses output of the secondary coil of the transformer as power for driving the control terminal of a switching element of the power converter. Specifically, to the secondary coil of the transformer, a series circuit, which is comprised of a pair of first and second capacitors connected to each other in series, is connected via a rectifier. That is, different first and second voltages are alternately applied, with a regular cycle, to the first and second capacitors, i.e. if in one cycle the first voltage is applied to the first capacitor and the second voltage is applied to the second capacitor, then in the next cycle, the second voltage is applied to the first capacitor and the second voltage is applied to the second capacitor. The first voltage means the potential across the first capacitor relative to the connection point between the first and second capacitors, and the second voltage means the potential across the second capacitor relative the connection point.
According to results of comparison between a reference voltage and the potential of the connection point between the first and second capacitors, a first drive signal with a high level and a second drive signal with a low level are alternately generated to be applied to a switching element of the power converter. While the first drive signal with the high level is being generated, the switching element is on, and while the second drive signal with the low level is being generated, the switching element is off. That is, the known power converter is configured to repeatedly turn on or off the switching element of the power converter.